Humidity and moisture from an indoor pool can damage not only internal building materials, but also permeate the interior cavity of pool structure (between inner wall and outer wall of the pool room). Without the proper vapor retarder, moisture from the pool can migrate into these areas as air passes from the interior warm side of the pool room to the colder outdoor air side.
Mold, rot, mildew, internal premature structural failure, decay, and deterioration of insulation are some of the problems when vapor retarders are not installed, or penetrated after installation. Vapor Barriers are often overlooked in the design stages, forgotten, not installed, or installed improperly.
Green Board, Dryvit, various other “boards”, foil faced insulation and other types of sprayed-in-place urethane foam insulation are not considered vapor barriers, nor are generally recommended. There are very few acoustical ceiling tiles that are made to withstand the stratification of humidity in an indoor pool. Drop ceilings are discouraged as they become moisture traps in swimming environments. Many of these types of materials have been used in the past with extremely negative results; they are not bullet proof when it comes to moisture damage. Therefore, with an effective vapor retarder, good insulation, negative pressure and a properly designed pool room dehumidification system; moisture damage can be prevented in the design/construction stages.
Generally, Vapor Barriers for an indoor pool are materials that do not permit moisture to migrate passed the surface areas into the structure. They are generally heavy plastic sheeting in 8, 10 or 12 mil. The effectiveness of the barriers to prevent moisture migration is rated by “permeability ratings”. The higher the perm rating, the less moisture will penetrate the barrier into the pool room structure. It is recommended the barrier have a perm rating of 0.10 or less when utilized in an indoor pool.
If an existing indoor pool and a vapor retarder cannot be installed under finished surfaces, other materials that can be considered vapor retarders are waterproof paints or other types of paints or sealants (check with a paint specialty or building professional). We also recommend reviewing ASHRAE Guidelines on vapor barriers for additional information.
The application of your vapor barrier is also critical to preventing moisture damage. The Vapor Barrier for all natatoriums is installed in the walls and ceilings under the finished surface (or the warm side of the pool room). We recommend 10-12 mil. seamless vapor barriers be installed by enveloping the entire pool room. The barrier is overlapped and sealed at the joints. Once installed, avoid penetrations of the barrier (i.e. top-hat recessed can lighting is not recommended; surface mount all lighting). All penetrations by mechanical and electrical contractors must be sealed air tight. It is recommended the wall vapor barrier be sealed (not just overlapped) to the ceiling vapor barrier.
Care must also be exercised in installing insulation around the pool enclosure, since poor insulation leads directly to higher energy and operating costs. Note that gaps in insulation create “cold spots” that promote moisture condensation as well. If negative pressure is not designed, moisture can and will migrate into areas outside of the pool room. A properly designed indoor pool will ensure attention to these three important aspects of moisture migration and humidity control.